According to various requirements from customers, known semiconductor packages have various package configurations. One type of semiconductor packages is that a flip chip is mounted on a leadframe. There are a plurality of bumps formed on active surface of a flip chip to connect a plurality of leads in replacement of bonding wires for inner electrical connection within a molding compound. However, the leadframe provided for flip-chip connection is slightly different from conventional leadframe for wire-bonding connection. The leadframe has a plurality of appropriate bump-bonding regions at the fan-in end of leads corresponding to the bumps of the flip chip. However the bumps will easily wet other portions of the leads during reflowing process.
Flip-chip typed QFN packages (Quad Flat Non-leaded package) are disclosed in U.S. Pat. No. 6,507,120 (which R.O.C. Taiwan Publication Patent number is 463,342). The package mainly comprises a plurality of leads from a leadframe, a flip chip bonded to the leads via a plurality of bumps, and a molding compound for encapsulating the flip chip. A solder mask is formed on upper surfaces of the leads and has a plurality of openings corresponding to the bumps to limit the bump-bonding regions of the leads. However, the well-known solder mask is generally formed over a substrate or a printed circuit board by printing technique and covers the resin layer of substrate between traces. When the solder mask is printed on the upper surfaces of the leads, the consumption of solder mask is very large because that the thickness of the leads is much thicker than that of the well-known traces of a substrate. Moreover, since there is no supporting resin layer below the leads, a solder mask is hard to form and easily contaminates the leadframe and processing machine. Besides, the flip chip typed QFN is used for packaging as CSP (Chip Scale Package) only because the leads are quite short without fan-out design. Furthermore, the bonding strength between the leads coated with solder masked and the molding compound is weak. As a result, the leads are easily delaminated from the molding compound and short circuit occurs.